Dampering systems

ABSTRACT

A chimney-dampering system for regulating the pressure in a furnace includes a circumferential lip in the chimney for deflecting inwardly gas rising up the chimney adjacent its wall, and a nozzle pointing centrally downwardly to direct dampering air downwardly through the aperture defined by the lip.

United States Patent Inventors Appl. No.

Filed Patented Assignee Priority Clifford Inrnan Penketh, near Warrington, Lancashire; David George Cadwell, Skelmersdale, Lancashire, both of, England 833,010

June 13, 1969 June 15, 1971 Pilkington Brothers Limited Liverpool, England June 18, 1968 Great Britain DAMPERIN G SYSTEMS 11 Claims, 4 Drawing Figs.

US. Cl

263/40, 1 10/160 lnt.C|. F271) 3/02, F231 11/02 [50] Field of Search 263/40, 15; 1 10/160 [56] References Cited UNITED STATES PATENTS 1,635,939 7/1927 lsley 110/160 X 2,979,322 4/1961 Dailey, Jr. 263/40 3,373,007 3/1968 Ticknor 236/15 C Primary Examiner-John J. Camby AttorneyMorn'son, Kennedy & Campbell ABSTRACT: A chimney-dampering system for regulating the pressure in a furnace includes a circumferential lip in the chimney for deflecting inwardly gas rising up the chimney adjacent its wall, and a nozzle pointing centrally downwardly to direct dampering air downwardly through the aperture defined by the lip.

PATENTEDJUNISIQYI 3584851 SHEET 1 [1F 3 Inventor: CLIFFORD INMAN and DAVID GEORGE CADWELL %M, M g 1% PATENTED m1 519?: 3; 5841851 SHEET 2 [1F 3 v lnuenlor: CLIFFORD INMAN and DAVID GEORGE- CAUNELL PATENTEDJUNISIQYI 3584.851

SHEET 3 [1F 3 iOi lrwenlor: CLIFFORD INMAN and DAVID GEORGE CADWELL DAMPERING SYSTEMS BACKGROUND OF THE INVENTION This invention relates to a chimney-dampering system, more especially for use with a furnace chimney embodying a recuperator which extracts heat from the hot gases rising up the chimney.

In a recuperator, hot waste gases from a furnace rise up a chimney, which passes through a heat exchanger, and it has been proposed to provide a dampering system wherein air is introduced downwardly into the chimney top through nozzles whose orifices are equispaced round the inside of the chimney at a position substantially level with the chimney top. With such a system the furnace pressure can, to some extent, be controlled by the dampering air supplied through the nozzles, but such control has been found not to be satisfactory. In particular, the control is very dependent on the correct positioning of parts at the top of the chimney, and condensates tend to collect in this region during use, thereby reducing the degree of control which can be achieved and affecting the characteristics of the system.

It is a main object of the present invention to provide improved control over the furnace pressure by the dampering air.

SUMMARY According to the present invention there is provided a chimney-dampering system in which the chimney is provided with an inwardly projecting circumferential lip adapted to deflect inwardly gas rising up the chimney adjacent its wall, and a single nozzle disposed with its orifice pointing centrally down the chimney to direct dampering air centrally downwards through the chimney aperture defined by the lip so that in operation dampering air supplied to the nozzle is introduced downwardly into the chimney at a speed sufficient to make substantial ingress past said lip and to effect recirculation ofgases in the chimney below the lip.

It has been found that, with such a dampering system, control over the furnace pressure and over the extraction of heat from waste gases in the recuperator can be greatly improved, thereby improving the efficiency of the furnace.

In a preferred embodiment of the invention the nozzle orifice is spaced above the level of the top of the chimney, and a wind shield is provided around the top of the chimney to shield the nozzle and the chimney top.

The invention also comprehends a furnace, for example a glass melting furnace, having a recuperator chimney with a dampering system as defined above.

Further the invention provides a method of operating a furnace having a chimney for exhaust gases, characterized by deflecting inwardly gas rising up the chimney adjacent its wall, and supplying dampering air centrally downwardly into that deflected air at a rate such as to effect recirculation of gasses in the location where rising gas is deflected inwardly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic side elevation, partly in section, of the upper part ofa recuperator chimney, fitted with a chimney dampering system according to the invention,

FIG. 2 is a view similar toFIG. l ofa modified arrangement.

DESCRIPTION OF THEPREFERRED EMBODIMENT Referring to FIG. 1, a substantially cylindrical vertical recuperator chimney l is formed at its top edge with an inwardly projecting horizontal circumferential lip 2 which acts to deflect inwardly hot gas 3 rising up the chimney adjacent its wall. A nozzle 4 which is held in a collar 5 fixed by struts 6 to the top of the chimney is directed downwardly and centrally into the chimney and is disposed with its outlet orifice 7 substantially coaxial with the chimney, in the embodiment illustrated.

Dampering air is supplied from a manifold 8 through a butterfly valve 9 to the nozzle 4 and is released through the orifice 7 ofthe nozzle into the top of the chimney 1 at a speed sufficient to cause the dampering air, indicated at 10, to make substantial ingress into the chimney and thereby effect, in combination with the deflecting. action of the lip 2, recirculation of the gas in the upper portion of the chimney below the. lip 2 as indicated by the arrows 11. The arrows 12 indicate the hot waste gases rising from a furnace connected to the recuperator. The furnace pressure is controlled by controlling the velocity pressure of the dampering air 10 released from the nozzle 4. That is, a required change .in the furnace pressure can be effected by adjusting the valve 9 to cause a predetermined change in the volume of dampering air introduced and, conversely, undesired deviations in the furnace pressure can be corrected by control of the dampering air. It has been found that a dampering system as shown in FIG. 1 provides an effective and reliable furnace pressure control.

In the embodiment illustrated in FIG. 1 the orifice 7 of the nozzle 4 is substantially level with the top lip 2 of the chimney. It has been found'that even better control can be achieved by raising the nozzle orifice above the top of the chimney and lip, as shown in FIGS. 2 and 3.

The optimum height of the nozzle is dependent on the conditions of the system, and can readily be found by a process of trial and error. Conveniently, as shown in FIG. 2, a duct 13 leads to the nozzle 4 from a butterfly valve 14 which is connected to an air supply manifold, not shown. The duct 13 includes a telescopic section 15 which, facilitates raising and lowering of the nozzle, and also holds firm the upper part of the duct 13 which terminates in the nozzle.

In this embodiment in which the nozzle is spaced above the top of the chimney it is desirable to shield the dampering air issuing from the nozzle from crosswinds. For this purpose a wind shield or skirt is provided. The wind shield has a floor 16 which is fixed, as indicated at 17, to the chimney, and upstanding sidewalls 18 which rise to a height such that the top of the walls 18-is at least as high as the nozzle orifice 7.-The walls 18 may be higher if particularly windy conditions are experienced. The wind shield illustrated is of square-cross section (see FIG. 3) but any suitable shape may be, used, for example an octagonal shape.

It will be appreciated that the dimensions of the parts, and the velocity of dampering airflow are chosen to provide the optimum practicable control in relation to the conditions subsisting in any particular system. In the particular system shown in FIGS. 2 and 3 the diameter of the chimney l is 36 inches, and the orifice 7 of the nozzle has a diameter of 4 inches. Air is supplied through the manifold to the valve 14 by a fan supplying 2,400 cubic feet of air per minute at 8 inches water gauge. By means of the valve 14 the flow of dampering air can be controlled, for example by a computer which sets the valve in derived from a transducer connected to the furnace head-- space, as illustrated in FIG. 4.

It was found that with a lip 2 of 6 inches width (in practice provided by a cover plate having a central aperture of diameter 24 inches), and with the orifice 7 of the nozzle 2 feet 6 inches above the top of the chimney, oscillations of about 0.007-inch water gauge about a mean furnace pressure of 0.065-inch water gauge were experienced with the butterfly valve 14 approximately 50 percent open. With the nozzle orificeraised to 3 feet 0 inches above the top of the chimney, the amplitude of the oscillations was reduced to 0.005 inches water gauge, the butterfly valve s'etting moving between 47 percent to 54 percent open to effect control. Raising the nozzle orifice a further 6 inches to 3 feet 6 inches above the.top of the chimney was found to increase the amplitude of the oscillations.

The above values were found in substantially normal, i.e. not unduly strong, wind conditions. In the same wind conditions, an arrangement using a cover plate with an aperture of diameter 20 inches (i.e. a lip 2 of 8 inches width) and with the nozzle orifice 2 feet 6 inches above the lip, was found to give oscillations of 0.010-inch water gauge about a mean furnace pressure of 0.065-inch water gauge with the butterfly valve 14 slightly less than 20 percent open. With a cover plate having an aperture of 28 inches diameter (i.e. a lip 2 of 4 inches width), and with the same height of nozzle orifice, it was found that, even with the butterfly valve 14 fully open, the furnace pressure did not rise above 0.03-inch water gauge.

In these tests the wind shield had a height such that the top of the walls 18 was approximately 1 foot above the level of the orifice 7.

From the above it will be seen that, in normal wind conditions, it was found that the preferable arrangement, with the butterfly valve 14 about 50 percent open, i.e. midway along its setting range, was provided with the cover plate having a 24- inch diameter aperture and with the nozzle orifice 3 feet inches thereabove. ln windy, and particularly in gusty conditions with sudden changes in wind direction, it was found that, although temporary variations in furnace pressure might occur, satisfactory control was quickly regained with this arrangement.

Under strong wind or gale conditions, with the butterfly valve fully open, the nozzle was lowered to 2 feet 6 inches above the chimney top and the dampering air supply to the nozzle was boosted by incorporating a further fan in tandem with the main fan. It was found, however, that under such strong wind or gale conditions a cover plate having an aperture of 20 inches diameter, with the nozzle orifice 2 feet 6 inches above the top of the chimney was preferable. With this latter arrangement the butterfly valve 14 was about 20 percent open for normal operation, that is to maintain a mean furnace pressure of 0.065-inch water gauge. Such a normal setting, towards the closed end of the valves range, was not found to be disadvantageous since a requirement for substantial movement of the valve in the closed direction is unlikely, and a large scope for movement in the open direction to combat circumstances requiring the introduction of a greater volume of dampering air is made available.

The chimney-dampering system may be located part way down the chimney if a tall chimney is provided. The location of the lip and nozzle in such circumstances is such as to permit adequate response in the regulation of the furnace pressure.

It has further been found that with the system described above no undue collection of condensate material on the lip 2 or nozzle 4 sufficient to upset the operating and control characteristics of the system occurred.

FIG. 4 shows schematically a glass melting furnace 19 which feeds molten glass to a forehearth, indicated generally as 20, which feeds bushings from which glass streams are attenuated to produce glass fibers in well known manner. The furnace has a chimney 21 with an associated recuperator 22, which provides a heat exchange between hot exhaust gases from the furnace rising up the chimney 21 and incoming air fed through the recuperator 22 to be combined with fuel for burners in the furnace. A chimney-dampering arrangement as described above, and generally indicated as 23, is mounted at the top of the chimney. Dampering air is fed to the nozzle arrangement from a fan 24 through a butterfly valve 25.

A pressure-sensitive probe or transducer 26 is fitted in a wall 27 of the furnace 19 at the outlet end of the furnace to detect the pressure in the furnace headspace above the molten glass, and to emit a signal indicative of the detected pressure to a control unit 28. An ambient air pressure detector device 29 is positioned outside the furnace at the same level as the probe 26 and also emits a pressure indicative signal to the control unit 28. This latter signal provides a reference which permits compensation for ambient or atmospheric pressures outside of the furnace. The control unit 28 compares the detected pressure in the furnace with preset values and emits a control signal indicative of the setting of the valve means 25 required to give a supply of dampering air to the nozzle arrangement 23 such as to achieve a desired preset pressure in the furnace. Such control signal serves to effect automatic adjustment of the valve means 25 as necessary.

If desired the control signal emitted by the control unit 28 may, instead of regulating the valve 25, be used to regulate the operation of the fan 24 such as to achieve the required supply of dampering air. It has been found, however, that regulation of the valve permits a simpler and less expensive arrangement.

We claim:

1. A chimney-dampering system including an inwardly projecting circumferential lip fixed within the chimney to define a central chimney aperture and to deflect inwards gas rising up the chimney adjacent its walls, a single nozzle disposed with its orifice pointing centrally down the chimney and positioned to direct dampering air centrally downwards through the chimney aperture and means for regulating air supply to the nozzle so that in operation dampering air supplied to the nozzle is introduced downwards into the chimney at a speed sufficient to make substantial ingress past said lip and to effect recirculation ofgases in the chimney below the lip.

2. A chimney-dampering system according to claim I, wherein the lip is provided at the top of the chimney and the nozzle is fixed centrally to the top of the chimney to introduce dampering air downwardly into the top of the chimney.

3. A chimney-dampering system according to claim 2, wherein a windshield is provided around the top of the chimney to shieldthe nozzle and the chimney top.

4. A chimney-dampering system according to claim 1, wherein the nozzle orifice is spaced above the level of the circumferential lip.

5. A chimney-dampering system as claimed in claim 1, comprising recuperator means associated with the chimney and positioned at a level below the circumferential lip in the chimney.

6. A chimney-dampering system according to claim 1, associated with a furnace chimney, and including flow control means controlling the supply of dampering air to the nozzle in response to an indication of furnace pressure.

7. A system as claimed in claim 6, comprising pressure detector means in the furnace to detect the pressure within the furnace and to emit a signal indicative thereof, a valve in the air supply to the nozzle, and valve control means connected to said pressure detector to receive said pressure indicative signal and regulate the valve in response to that signal.

8. A system according to claim 7, wherein the furnace is a glass melting furnace, and the pressure detector means is located in the furnace near its outlet end to detect the pressure in the molten glass in the furnace.

9. A method of operating a furnace having a chimney for exhaust gases, characterized by deflecting inwards gas rising up the chimney adjacent its walls, supplying dampering air centrally downwards into that deflected air, and regulating the rate of supply of dampering air to effect recirculation ofgasses beneath the location where rising gas is deflected inwards.

10. A method as claimed in claim 9, wherein gas rising up the chimney adjacent its wall is deflected inwards at the top of the chimney and dampering air is supplied centrally downwards into the top of the chimney at a rate to make substantial ingress into the chimney and to effect recirculation of gasses in the upper part of the chimney.

11. A method as claimed in claim 9, of operating a glass melting furnace, comprising detecting the pressure in the headspace over the molten glass in the furnace and regulating the supply of dampering air in response to pressure variations to maintain constant pressure in the headspace. 

1. A chimney-dampering system including an inwardly projecting circumferential lip fixed within the chimney to define a central chimney aperture and to deflect inwards gas rising up the chimney adjacent its walls, a single nozzle disposed with its orifice pointing centrally down the chimney and positioned to direct dampering air centrally downwards through the chimney aperture and means for regulating air supply to the nozzle so that in operation dampering air supplied to the nozzle is introduced downwards into the chimney at a speed sufficient to make substantial ingress past said lip and to effect recirculation of gases in the chimney below the lip.
 2. A chimney-dampering system according to claim 1, wherein the lip is provided at the top of the chimney and the nozzle is fixed centrally to the top of the chimney to introduce dampering air downwardly into the top of the chimney.
 3. A chimney-dampering system according to claim 2, wherein a windshield is provided around the top of the chimney to shield the nozzle and the chimney top.
 4. A chimney-dampering system according to claim 1, wherein the nozzle orifice is spaced above the level of the circumferential lip.
 5. A chimney-dampering system as claimed in claim 1, comprising recuperator means associated with the chimney and positioned at a level below the circumferential lip in the chimney.
 6. A chimney-dampering system according to claim 1, associated with a furnace chimney, and including flow control means controlling the supply of dampering air to the nozzle in response to an indication of furnace pressure.
 7. A system as claimed in claim 6, comprising pressure detector means in the furnace to detect the pressure within the furnace and to emit a signal indicative thereof, a valve in the air supply to the nozzle, and valve control means connected to said pressure detector to receive said pressure indicative signal and regulate the valve in response to that signal.
 8. A system according to claim 7, wherein the furnace is a glass melting furnace, aNd the pressure detector means is located in the furnace near its outlet end to detect the pressure in the molten glass in the furnace.
 9. A method of operating a furnace having a chimney for exhaust gases, characterized by deflecting inwards gas rising up the chimney adjacent its walls, supplying dampering air centrally downwards into that deflected air, and regulating the rate of supply of dampering air to effect recirculation of gasses beneath the location where rising gas is deflected inwards.
 10. A method as claimed in claim 9, wherein gas rising up the chimney adjacent its wall is deflected inwards at the top of the chimney and dampering air is supplied centrally downwards into the top of the chimney at a rate to make substantial ingress into the chimney and to effect recirculation of gasses in the upper part of the chimney.
 11. A method as claimed in claim 9, of operating a glass melting furnace, comprising detecting the pressure in the headspace over the molten glass in the furnace and regulating the supply of dampering air in response to pressure variations to maintain constant pressure in the headspace. 